Thank you very much for all your help.
Armed with your information. It turned out that it was the transformer in both the original one, and the spare (fault finding control) boxes that I fitted were unserviceable.
I replaced the control box with a brand new one, and the burner sparked up and...
Thank you in advance for the time and advice.
My riello burner has stopped working, there dose not seem to be a spark on start up, but there is oil spraying out of the nozzle and the fan is running up. I have replaced the photo cell, and fitted a spare control box that I have used for fault...